Various types of manually operated presses have long been known in the art and have provided for more or less satisfactory operation. Many of these presses are used for photographic processing and other applications where heat and pressure are desired and have included electrical heating elements and generally are operated by some form of toggle mechanism. While this structure has generally proved rugged and reliable, it has lacked the capability of providing for a readily adjustable predetermined force to be exerted against objects of varying thicknesses placed between the platen and the base of the presses. On the other hand, presses which have provided for such adjustable predetermined forces frequently have been complex and expensive to manufacture, as well as difficult to adjust.